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Shares of Sangamo Therapeutics, Inc. SGMO increased 1.1% following the presentation of promising new data from phase I/II Alta study evaluating its gene therapy, SB-525, in patients with severe hemophilia A. Sangamo is developing the gene therapy candidate in collaboration with Pfizer PFE.

The data were presented at the Congress of the International Society on Thrombosis and Haemostasis (“ISTH”) in Australia.

Sangamo’s shares have gained 0.3% so far this year compared with the industry’s increase of 3.8%.

The phase I/II study is evaluating four doses of SB-525 — 9e11 vg/kg, 2e12 vg/kg, 1e13 vg/kg and 3e13 vg/kg. Updated data from the study showed that two patients treated with the highest dosage (3e13 vg/kg) achieved normal factor VIII levels, with no bleeding event, which continued for 19 and 24 weeks. Moreover, two new patients enrolled in the highest dosage cohort also demonstrated similar factor VIII activity kinetics consistent with the first two patients at week four and six. The company will soon initiate dosing of the fifth patient in the highest dosage cohort.

The fact that the highest dose of SB-525 achieved normal factor VIII levels within five to seven weeks probably encouraged investors. However, the sustainability of this level remains to be seen. Data available so far showed that normal levels of factor VIII were sustained for 24 weeks in the highest dose cohort. Moreover, one patient receiving 1e13 vg/kg of SB-525 has shown durable factor VIII level for 52 weeks.

Please note that there are several other pharma/biotech companies developing gene therapies for treating hemophilia A. The most advanced gene therapy for hemophilia A treatment in clinical studies is BioMarin’s valoctocogene roxaparvovec (BMN-270). Late-stage studies are evaluating 6e13 vg/kg and 4e13 vg/kg doses of the candidate. BioMarin’s candidate has also achieved durable factor VIII levels in patients. BioMarin will file regulatory applications seeking approval of valoctocogene roxaparvovec for severe hemophilia A in both the United States and EU in the fourth quarter of 2019. Other companies developing gene therapy candidates for treating hemophilia A include Spark Therapeutics ONCE and uniQure QURE.

Although Sangamo is a long way from commercialization of SB-525, the candidate has demonstrated better improvement in factor VIII levels compared to BioMarin’s gene therapy candidate. The promising data from the early stage study on SB-525 resulted in a decline in shares of BioMarin and Spark on Jul 8.